Conventional imaging photodetection devices are disclosed for example in Non-Patent Documents 1 and 2. The imaging photodetection devices disclosed therein will be described below in brief.
FIG. 17A is a side view showing a schematic configuration of a conventional imaging device. A light beam such as natural light enters an object 1, and the light beam reflected thereby forms an image 3 on a photodetection device 4 such as a CCD or a CMOS through a lens system 2. Though the lens system 2 is composed typically by combining a plurality of lenses aligned along an optical axis in order to ensure the optical performance, the lens system 2 is shown schematically as a single lens in FIG. 17A.
FIG. 17B is a magnified cross-sectional view of a portion XVIIB in FIG. 17A, showing a schematic configuration of the photodetection device 4. A transparent low refractive index buffer layer 7 made of SiO2 or the like, a transparent high refractive index buffer layer 8 made of SiN or the like, a plurality of color filters 9 and a plurality of microlenses 10 are laminated in this order on a detection substrate 5 where a plurality of photodetectors 6 have been formed. An uneven structure is provided on a surface 7a of the transparent buffer layer 7 in contact with the transparent buffer layer 8 so that the thickness of the transparent buffer layer 7 is reduced at each of the photodetectors 6. In contrast, a surface 8a of the transparent buffer layer 8 in contact with the color filters 9 is planar.
The microlenses 10 are arranged at the respective intersections of an orthogonal grid, and one color filter 9 and one photodetector 6 are arranged on the central axis of each microlens 10.
The microlenses 10 function so as to refract light such as a light beam 11a′ that enters with a shift relative to the central axis of the microlens 10 and guide the light to the photodetector 6. The uneven structure on the surface 7a of the transparent buffer layer 7 also has a lens effect, thereby refracting a divergent light beam 11b′ that travels in a direction away from the center of the photodetector 6 and guiding it to the photodetector 6.
The color filters 9 are composed of three kinds of filters, namely, a red transmission filter 9R, a green transmission filter 9G and a blue transmission filter 9B. The red transmission filter 9R has a light transmission characteristic (spectral sensitivity characteristic) of cutting (absorbing) light of a wavelength other than red, as illustrated with a curve R in FIG. 18; the green transmission filter 9G has a light transmission characteristic (spectral sensitivity characteristic) of cutting (absorbing) light of a wavelength other than green, as illustrated with a curve G in FIG. 18; and the blue transmission filter 9B has a light transmission characteristic (spectral sensitivity characteristic) of cutting (absorbing) light of a wavelength other than blue, as illustrated with a curve B in FIG. 18 (see Non-Patent Document 2). A color pixel for detecting color image information is configured with four color filters 9 composed of the red transmission filter 9R, the green transmission filter 9G, the blue transmission filter 9B, and a green transmission filter 9G for brightness detection, and also four photodetectors 6 corresponding to the color filters 9. An array of the photodetectors 6 corresponding to the four color filters 9 is shown in FIG. 19. In FIG. 19, R indicates a photodetector corresponding to the red transmission filter 9R and detecting a red color, G indicates a photodetector corresponding to the green transmission filter 9G and detecting a green color, and B indicates a photodetector corresponding to the blue transmission filter 9B and detecting a blue color. One color pixel 19 is configured with four basic pixels forming 2 columns×2 rows in which two green pixels (basic pixels G) are arranged at one pair of opposing corners and one blue pixel (basic pixel B) and one red pixel (basic pixel R) are arranged at the other pair of opposing corners. This array is referred to as a Bayer array, and is advantageous in that a color pixel 19′ can be formed also at a position obtained by shifting in the vertical direction (X-axis direction) or the horizontal direction (Y-axis direction) by half the size of the color pixel 19 (the size of a basic pixel). Accordingly, the resolution is improved to half the size of the color pixel 19 (¼ the area of the color pixel 19), that is, the size of a basic pixel.
FIG. 20 is a magnified plan view of a detection plane of the optical detection device 4. The plurality of photodetectors 6 are arranged at the intersections of the orthogonal grid in a state spaced away and insulated from each other. Between the photodetectors 6 adjacent horizontally to each other, a plurality of vertical transfer CCDs 17 as signal wires extending vertically are provided, and the plurality of vertical transfer CCDs 17 are connected to a horizontal transfer CCD 18 as a signal wire extending horizontally. Light focused by the microlens 10 is received by the photodetector 6 located directly below the microlens 10, and photoelectrically converted. Electric charge stored in the photodetector 6 is sent to the vertical transfer CCDs 17 and further sent to the horizontal transfer CCD 18 so as to be output as an image signal.
In the photodetection device 4 as shown in FIG. 17B, the color filters 9 are used to let light of a specific color enter each of the photodetectors 6. On the other hand, a photodetection device as shown in FIG. 21 is suggested, which uses a microprism 31 in order to disperse a light beam 30 coming from a photographic subject and transmitted through a microlens (not shown), and detects the light beams of respective colors of red (R), green (G) and blue (B) with photodetectors 32R, 32G and 32B (see Patent document 1).
Citation List
Patent Document
Patent Document 1: JP 2002-502120A (Tokuhyo)
Non-Patent Documents
Non-Patent Document 1: ‘Optical and Electro-Optical Engineering Contact’, vol. 40, No. 1 (2002), p. 24
Non-Patent Document 2: ‘Transistor Gijutsu’, February 2003, p. 128